Normally, the optical low pass filter is made of two or more pieces of quartz crystal plates and located in front the CCD sensor. The beam of the target image information generates birefringence after paving the OLPF. Based on the pixel size of the CCD and the total photosensitive area, the sampling cut-off frequency is calculated and the separation distance between the o light and the e light can also be calculated. Changing the incident beam will form a target frequency with a difference frequency, so as to achieve the purpose of reducing or eliminating low-frequency interference fringes, especially, pseudo-color interference fringes occurred in color CCD.
In addition, when color scenes are photographed using a CCD or a CMOS image sensor, since the response of the image sensor to colors is different from that of the human eyes, it is necessary to remove the infrared part which can be detected by the image sensor but cannot be detected by the human eyes, and adjust the response to the colors in the range of visible lights, so that the colors presented in the images are in line with the feeling of the human eyes. Therefore, a piece of infrared absorbing glass is generally added in the middle of the OLPF chip to obtain excellent results. However, the thickness of the product is increased.
Therefore, how to thin the optical low pass filter is a problem to be solved urgently.